The present invention relates to a method of manufacturing a thin compound oxide film used in a light modulation element, a piezoelectric element, a surface acoustic wave element, an oxide superconductor element, an LSI, and an EL and an apparatus for manufacturing a thin oxide film.
A known conventional method of manufacturing a thin compound oxide film is a sputtering method. In this method, epitaxial growth of the thin film can be performed to prepare a single-crystal composite oxide such as PZT[Pb(ZrTi)O.sub.3 ], PLZT[(PbLa)(ZrTi)O.sub.3 ], PbTiO.sub.3, and BaPb.sub.1-x Bi.sub.x O.sub.3.
Successful examples of the methods of sputtering thin compound oxide films are limited to those for a limited number of oxides described above. Since control of the oxygen content depends on an oxygen partial pressure, control on the atomic level cannot be accomplished. Good reproducibility cannot be assured due to change in a target composition ratio with time. Thus, oxygen defects are formed in the resultant thin film, density of the film is lowered, or composition errors occur. Therefore, thin films required in other various fields of applications cannot be obtained. In addition, according to a conventional sputtering method, a gas is adsorbed on the surface of the substrate. In order to epitaxially grow atomic particles bombarding the surface of the substrate, atoms deposited on the substrate must be moved to a proper crystal site and must be aligned. However, such movement of atoms is prevented by the adsorbed gas. In the case of an oxide film, oxygen atoms for forming an oxide in addition to the adsorbed gas prevent movement of the deposited atoms. For these reasons, the substrate must be heated to a temperature of 500.degree. C. or higher. As a result, film constituting elements are undesirably diffused into the under-layers if they are multilayered films having different materials.
Another conventional technique for forming a thin film is to deposite a material onto a substrate and at the same time to implant oxgen ion beams, as described in "ion-beam-assisted deposition of thin films" (APPLIED OPTICS, Vol. 22, No. 1, Jan. 1, 1983, P. J. Martin et al.) and "Review ion-based methods for optical thin film deposition" (JOURNAL OF MATERIALS SCIENCE 21 (1986) PP. 1-25, P. J. Martin).
The former literature deals with a thin film of an oxide of a simple substance such as TiO.sub.2, unlike in the thin film of a compound oxide according to the present invention. In addition, energy of an ion beam is as high as 600 to 750 eV, and the resultant thin film tends to be amorphous. In the latter literature, since an operation gas pressure of an ion source is 1.times.10.sup.-4 Torr or more, no deposition is performed in a high vacuum. Deposition molecules of the material repeatedly collide with a residual gas and reach the substrate. Therefore, no controlled molecular beam can be obtained. In addition, adsorption occurs on the substrate surface due to a residual gas. Therefore, an initiation temperature of epitaxial growth is undesirably increased. Energy of the oxygen ion beam incident on the substrate adversely affects crystallinity of a thin film to be formed. Selective control of the energy range for preventing crystal defects cannot be performed. The implanted oxygen beam includes O.sup.+, O.sub.2.sup.+, O.sub.2.sup.++, and O (neutral). The accurate number of oxygen atoms incident on the substrate cannot therefore be controlled.